<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style lang="">
    .checklist {
      padding: 50px;
      position: relative;
      background: #043b3e;
      border-top: 50px solid #03a2f4;
    }

    .checklist h2 {
      color: #f3f3f3;
      font-size: 25px;
      padding: 10px 0;
      margin-left: 10px;
      display: inline-block;
      border-bottom: 4px solid #f3f3f3;
    }

    .checklist label {
      position: relative;
      display: block;
      margin: 40px 0;
      color: #fff;
      font-size: 24px;
      cursor: pointer;
    }

    .checklist input[type="checkbox"] {
      -webkit-appearance: none;
    }

    .checklist i {
      position: absolute;
      top: 2px;
      display: inline-block;
      width: 25px;
      height: 25px;
      border: 2px solid #fff;
    }

    /* 这样的处理方式 */
    .checklist input[type="checkbox"]:checked~i {
      top: 1px;
      height: 15px;
      width: 25px;
      border-top: none;
      border-right: none;
      transform: rotate(-45deg);
    }

    .checklist span {
      position: relative;
      left: 40px;
      transition: 0.5s;
    }

    .checklist span:before {
      content: '';
      position: absolute;
      top: 50%;
      left: 0;
      width: 100%;
      height: 1px;
      background: #fff;
      transform: translateY(-50%) scaleX(0);
      transform-origin: left;
      transition: transform 0.5s;
    }

    .checklist input[type="checkbox"]:checked~span:before {
      /* 注意这个scaleX 也是存在 方向处理的 */
      transform: translateY(-50%) scaleX(1);
      transform-origin: right;
      transition: transform 0.5s;
    }

    .checklist input[type="checkbox"]:checked~span {
      color: #154e6b;
    }
  </style>
</head>

<body>
  <div class="checklist">
    <h2>Item Checklist with CSS</h2>
    <label>
      <input type="checkbox" name="" id="" />
      <i></i>
      <span>Item #1</span>
    </label>
    <label>
      <input type="checkbox" name="" id="" />
      <i></i>
      <span>Item #2</span>
    </label>
    <label>
      <input type="checkbox" name="" id="" />
      <i></i>
      <span>Item #3</span>
    </label>
  </div>
</body>

</html>